Stabilized magnetic amplifier for an inductive d.-c. load



March 1, 1966 F. W. KELLEY, JR

STABILIZED MAGNETIC AMPLIFIER FOR AN INDUCTIVE D.C. LOAD Original Filed Oct. 27, 1960 A C SUPPLY T0 SOURCE OF CONTROL J3 SIG/VA L ATTORNEY United States Patent 3,238,468 STABILIZED MAGNETKI AMPLIFIER FOR AN INDUCTIVE D.-C. LOAD Fred W. Kelley, Jr., 1276 Hunt Club Lane, Media, Pa. Original application Oct. 27, 1960, Ser. No. 65,428.

Divided and this application Mar. 25, 1965, Ser. No.

2 Claims. (Cl. 330-8) This application is a division of my co-pending patent application Ser. No. 65,428, now Patent No. 3,191,117, filed October 27, 1960, and assigned to the same assignee.

The present invention relates to magnetic amplifiers of the self-saturating type having rectifiers connected in circuit with the gate windings of saturable reactor apparatus and generally known as amplista-ts. More particularly, the invention relates to amplistats supplying relatively high inductance D.-C. loads, and has for an object the provision of means for improving the operation of magnetic amplifiers of this character. A more specific object of the invention is to improve the operating stability of an amplistat when connected to an inductive D.-C. load.

Heretofore such amplistats have exhibited an inductive load snap action instability in their operating characteristics. The cause of instability and several proposed remedies for it are discussed in chapter 20, pages 320-40 of H. F. Storms well known book Magnetic Amplifiers (John Wiley and Sons, New York, 1955). The remedy that is most often used in the art today employs a commutating rectifier across the amplistat output terminals. If the commutating rectifier circuit exhibited ideal characteristics, i.e. zero forward resistance, this technique for averting instability would be completely satisfactory in all applications. In practice, however, commercially available rectifiers have finite forward impedances, and consequently this popular technique has not always had the desired effect.

Accordingly, a further object of this invention is the provision of improved amplistat circuitry in which snap action instability is virtually eliminated.

By way of summary account of the invention, there is provided a self-saturating magnetic amplifier having a magnetic core member, a gate winding mounted thereon, a rectifier connected in circuit with the gate winding, and two output terminals adapted to be connected to an inductive load. In order to avert inductive load induced snap action instability in the amplistat, a commutating rectifier is connected across the output terminals, and a feedback winding is included in circuit with this rectifier. The feedback winding is mounted on the aforesaid core member in degenerative polarity, whereby during conduction by the commutating rectifier degenerative ampere turns are produced in the feedback Winding to counteract in the core member the regenerative ampere-turn effect that will then be associated with gate winding conduction as a result of the finite forward voltage drop of said commutating rectifier.

The novel features which are believed to be characteristic of this invention are set forth with particularity in the appended claims. This invention, however, both as to its organization and method of operation together with further objects and advantages, may best be understood by reference to the following description taken in conjunction with the accompanying drawing in which the single figure is a simple schematic diagram of an embodiment of the invention.

Referring now to the drawing, the amplistat 42 therein shown is connected in a diametric configuration to supply D.-C. current to a highly inductive load 43. The amplistat comprises gate windings 44 and 45 which are connected to opposite terminals of the secondary winding 46a of a single-phase supply transformer 46. Uncontrolled rectifiers such as diodes 47 and 48 are connected between the gate windings and terminal 43a of the inductive load 43 of which the other terminal 43b is connected to the center tap of the supply transformer secondary winding. The gate winding 44 is mounted on one leg 49 of a core member, and similarly gate winding 45 is mounted on a leg 50 of another core member. Also mounted on the core members is a control winding having a coil 51 mounted on core leg 49 and a coil 52 mounted on core leg 50. These control Winding coils are illustrated as being connected in series relationship to a source of control signals.

Dots associated with the gate windings and the control windings indicate the winding polarities. That is, if a voltage is applied to a gate winding such that the dot end is positive with respect to the opposite end, the voltage induced in the associated control winding is positive at the dot end and negative at the opposite end.

The core members may be made of any one of a number of high flux density core materials having rectangular hysteresis loops, such for example as the grain oriented nickel-iron alloys and cold rolled silicon steel tape. One of these materials is known to the trade and sold under the trade name Deltamax.

In order to counteract the destabilizing effect of the highly inductive load, a series combination of a commutating rectifier 53 and a feedback winding comprising series connected coils 54 and 55 is connected in a circuit across the output or load terminals of the amplistat. The feedback coil 54 is mounted on core leg 49 and feedback coil 55 is mounted on core leg 50. These coils carry the current of the commutating rectifier and are connected in such polarity that they produce degeneration of the amplistat as shown by the polarity dots associated with the gate winding coils 44 and 45 and with the feedback winding coils. The commutating rectifier is connected so that it blocks in the direction of current flow from the positive output terminal of the amplistat to the negative output terminal; in other words the cathode of the commutating rectifier is connected to the positive output terminal and the anode of the commutating rectifier is connected to the negative output terminal.

For complete elimination of inductive load instability the total number of turns of the feedback winding coils should be in the range between 5% and 10% of the number of turns of the gate windings. By means of the commutating rectifier and degenerative feedback combination, elimination of snap-action instability due to inductive load is accomplished with only a slight reduction in gain and a correspondingly slight reduction of the quantity known as the amplistats figure of merit which is defined as a fraction of which the numerator is the power gain of the amplistat and the denominator is its time constant.

Although a particular embodiment of the invention has been shown and described various modifications and changes will readily occur to those skilled in the art without departing from the true spirit of the invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Stabilized full-wave magnetic amplifying apparatus for use with an inductive D.-C. load comprising output terminals for connection to an inductive D.-C. load, a pair of self-saturating magnetic amplifiers each having a magnetic core member and a gate winding mounted thereon, means including a pair of rectifiers respectively associated wth the gate windings of said amplifiers for interconnecting said gate windings and said output terminals, and means for counteracting inductive load induced snap action instability comprising a commutating rectifier and a pair of feedback windings serially connected across said output terminals, said feedback windings being respectively mounted on the core members of said amplifiers in degenerative polarity.

2. Stabilized magnetic amplifying apparatus for use with an inductive load comprising positive and negative output terminals for connection to an inductive load, a self-saturating magnetic amplifier having a magnetic core member with a gate winding and a direct-current energized control winding mounted thereon, means including a rectifier for connecting said gate winding to said output terminals, and means for counteracting inductive load induced snap action instability comprising a commutating rectifier connected in a circuit across said output terminals poled to block in the direction of current flow from said positive -to said negative terminal and a feedback winding included in series With said commutat- References Cited by the Examiner UNITED STATES PATENTS 2,516,563 7/1950 Graves 323-61 X 3,076,131 1/1963 \Veil 323-66 X 3,131,360 4/1964 Lundahl 3308 ROY LAKE, Primaly Examiner.

N. KAUFMAN, Examiner. 

1. STABILZIED FULL-WAVE MAGNETIC AMPLIFYING APPARATUS FOR USE WITH AN INDUCTIVE D.-C. LOAD COMPRISING OUTPUT TERMINALS FOR CONNECTION TO AN INDUCTIVE D.-C. LOAD, A PAIR OF SELF-SATURATING MAGNETIC AMPLIFIERS EACH HAVING A MAGNETIC CORE MEMBER AND A GATE WINDING MOUNTED THEREON, MEANS INCLUDING A PAIR OF RECTIFIERS RESPECTIVELY ASSOCIATED WITH THE GATE WINDINGS OF SAID AMPLIFIERS FOR INTERCONNECTING SAID GATE WINDINGS AND SAID OUTPUT TERMINALS, AND MEANS FOR COUNTERACTING INDUCTIVE LOAD INDUCED SNAP ACTION INSTABILITY COMPRISING A COMMUTATING 